That was a great concise explanation. Now how do I apply it to this system? Do I want a low Q for a broader rolloff and smooth transition from one band to the next or a high Q for a clear distinction between two adjacent bands? Can the Q be too high and leave gaps between the band settings?

Thinking out loud ... Well adjacent bands have overlap so a very low Q across adjacent band would end up like you had little separation control over these bands. You would have to put more/less gain to make an audible difference. A high Q would be make more of a peak/loss in a narrower band around the center freq, and not influencing the adjacent band.

On your stereo, the center freq of each band is never equally spaced e.g 500Hz, 1000Hz, 1500Hz,... because the lower frequencies have more power per hertz than higher frequencies. (Think of a subwoofer shaking the house; not so with higher freqs) So, ideally, the bands are set up to have the same amount of power in each band. Now use gain and adjustments to influence the sound of each band.

Notice the non linear, (logarithmic) relationship between the bands, This is so there the power in each band is similar.

The Q/gain settings: Our ears and our stock speakers are not efficient at the low frequency (and we like bass), so the lowest band is boosted +5. The Q=1 will boost above the 120 hz center and bleed into the 2nd band. The high Q and attenuated gain in the second band limits this bandís contribution. Band 1 and band 3 will bleeding into band 2, with band 2 having a minor bump around 500 hz because of the higher Q. But the bump is attenuated so it blend in with the 1st and 3rd bandís contribution into band2. The 5th band, the widest, has gain with a low Q. This keeps the gain across the band fairly wide across the whole band. A picture would be best but donít have the time.

So he has created the classic ROCK equalizer setting (High base, low mid, high upper mid/treble) but has used both the gain and Q settings to extend (low Q) and limit (higher Q) the extent of the gains to achieve the response provides a smoother transition across the bands and to maybe compensate for the speakers response as well.